This invention relates to an automatic recording fluorometer/densitometer, and more particularly to an automatic reference circuit for such an instrument.
A recording fluorometer/densitometer is used to analyze the optical characteristics of a sample such as a clinical electrophoresis plate.
U.S. Pat. Nos. 3,479,265 and 3,635,808 disclose thin film agarose sample plates which can be used as the electrophoretic medium. The thin film samples of these patents are particularly convenient for handling and storage.
These samples are analyzed by fluorometric or densitometric optical detection. One instrument for automatically making analyses of this type is described in U.S. Pat. No. 3,706,877. In such an instrument, the total area under the recorded analog curve is integrated, and this value is stored. Also, the area under selected peaks of the curve is determined by integration and this area is stored as a percent of the total area.
Integration, and other quantization of detected outputs such as this require that the output be referenced to a voltage which is usually zero. This voltage is called correction for zero offset. In such instruments, it is common to use the voltage output at the beginning of the scan as the zero offset correction voltage. However, it often happens that this does not produce a true zero because the voltage at the beginning of the scan may not be the true minimum in detector output during the scan.